Numerous types of exercise machines have been devised in an attempt to establish optimal resistance to a force applied by the user throughout the entire exercise routine and in such a way as to overcome the need for the use of different exercise equipment in carrying out different specific exercises either in building muscles or increasing strength and endurance. Exercise machines of the constant force or isotonic variety customarily employ free weights. However, at some point in the course of each repetition of an exercise, the force will necessarily vary due to the ballistic nature of a free weight: Generally, varying the weight or body leverage in and of itself does not permit maximum effort during each phase of a repetition or movement. In this relation, varying strength levels of different athletes determines the need for resistance in accordance with a given strength level. Research indicates the advantages and benefits of being able to establish or vary the resistance in accordance with the athlete's strength output throughout an entire exercise, not just a portion of that exercise, and which permits the athlete to train to failure well past the limits of normal isotonic resistance.
Isokinetic exerciser apparatus in which the resistance is proportional to the force exerted have become increasingly popular in terms of permitting variation of the resistance imposed through a particular exercise movement and in controlling that resistance to be at a particular level. Isokinetic exercisers typically employ a hydraulic control system, dynamic braking system or clutch; however, exercisers of this type have certain limitations with respect to establishing a uniform resistance over the entire exercise program, particularly at the onset or completion of a particular movement.
Other exercise machines have employed other mechanisms, such as, cams in an effort to establish optimal resistance over the entire range of movement, but in general such mechanisms have been found to be extremely limited in application and are capable of providing only an average of a typical user's force profile notwithstanding that the profile will vary as a function of speed and fatigue. Furthermore, in exercise machines of the type employing a pump-powered pneumatic or hydraulic system, difficulties have been experienced in permitting the force profile to vary with individual variations in force, speed and range of movement.
I have previously devised exercising apparatus in which a weight bar is mounted for pivotal movement on a beam member of fixed length which is mounted in adjustably spaced relation to a lifting beam, and an isokinetic device in the form of a hydraulic cylinder is operative to limit the rate of movement in either direction of the weight bar by means of a valve arrangement which will change the direction from which the cylinder is operative to offer resistance to the movement. In this relation, reference is made to my U.S. Pat. No. 4,357,010. Apparatus has been devised by others will either electronically or hydraulically control the rate of movement of the apparatus by varying amounts and other representative patents in this field are U.S. Pat. Nos. 4,863,726 to R. J. Wilson; 4,307,608 to R. E. Useldinger et al; 4,184,678 to E. R. Flavell et al; and 4,235,437 to D. A. Ruis et al. To my knowledge, however, no one has devised exercise apparatus which can meet any resistance demand of the athlete in terms of force, position and time as a function of the athlete's force output during a particular exercise routine and of the athlete's previously recorded effort for that routine and fail to offer the proper level of resistance during direction change transitions, especially transition from a negative or downstroke to a positive or upstroke during each cycle. With respect to the athlete's force output, the athlete should not be able to move through an position too easily but on the other hand should not be restricted by too much resistance. In terms of previous recorded effort, it is desirable to be able to preset the resistance for a current exercise from past sessions as well as to increase or lessen the resistance according to past performance.